Creakiest sort of athlete (3-6)
I believe the answer is:
ice-skater
'athlete' is the definition.
(ice-skater is a kind of athlete)
'creakiest sort' is the subsidiary indication.
'sort' is an anagram indicator.
'creakiest' anagrammed gives 'iceskater'.
'of' is the link.
(Other definitions for ice-skater that I've seen before include "Dean for one" , "One gliding over rink" , "Winter sportsperson" , "Torvill or Dean, say" , "Person gliding on frozen water" .)